### Dalton’s law of partial pressure

John Dalton visualised that in a mixture of gases, each component gas exerted a pressure as if it were alone in the container. The pressure of each gas in mixture is called partial pressure.

Dalton’s law of partial pressure: It states that : the total pressure of a mixture of gases is equal to the sum of the partial pressures of all the gases present.

P_total = P_1 + P_2 + P_3 …..From the Ideal gas law we can conclude this:

There is another important law to calculate the artial pressure from the mole fraction and total pressure.

P_a : partital pressure of gas a , X_a : mole fraction of gas a , P_total : total pressure of mixture

If there is a mixture of two gases A and B:

P_total = P_A + P_B P_total = \frac{n_A R T}{V} + \frac{n_B R T}{V} P_total = (n_A + n_B) /frac{RT}{V}now: if we divided P_A over P_total

\frac {P_A}{P_total} = \frac{n_A}{n_A + n_B} \frac{RTV}{RTV}

\frac {P_A}{P_total} = \frac{n_A}{n_A + n_B}

\frac{n_A}{n_A + n_B} = X_A (X_{A} : mole fraction)

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